There is now a substantial body of data which indicates that Campylobacter pyloridis (CP) is an important cause of gastritis around the world, that it persists in untreated individuals but responds to treatment with antibiotics, and that it is tenacious in that high rates of recrudescence are seen soon after treatment is discontinued. CP have also been implicated in peptic ulcer disease and epithelial dysplasia. However, a number of key questions remain open: 1. Are there safe, inexpensive antibiotics and/or colloidal bismuth preparations capable of being used for long periods of time which will erradicate CP from the gastric mucosa? 2. What is the rate of reinfection with CP and the recurrence of abnormal histological changes and dyspepsia symptoms following cessation of antimicrobial therapy? 3. Is uncomplicated CP-associated gastritis important in the pathogenesis of "non-ulcer dyspepsia"? These questions will be addressed in a nearly ideal Peruvian population (in which virtually all gastritis seems to be associated with CP infection) using a double-blind, placebo-controlled therapeutic trial with an effective antibiotic (selected rom several candidates in preliminary efficacy trials of CP clearance). A serious effort will be made to develop culturally-appropriate symptom self-reporting instruments that will have sufficient internal validity and sensitivity to reveal true effects of treatment.